1. Field of the Invention
This invention relates generally to the field of graphic arts and especially to graphic arts impression dies such as copper, magnesium, bronze or other non-ferrous metal/ferromagnetic laminated dies. It also relates to graphic arts impression die assemblies for use on various types of stamping or embossing apparatus, including sheet or web-fed graphic arts presses such as clamshell, vertical or horizontal presses, and to improved processes for preparing the graphic arts impression dies and to preparation of impression graphic arts die assemblies. As used herein, the term graphic arts xe2x80x9cimpression die(s)xe2x80x9d means at least the categories of graphic arts dies including hot foil stamping/blocking dies, embossing dies, debossing dies, embossing/debossing dies, combination/fluted/one-shot/foil embossing dies, and any other graphic arts dies which combine any one or more of these general types of die functions on a single plate for smooth, lenticular, textured or grained surfaces, or any other similar graphic arts metal, polymeric or composite impression dies.
More particularly, the invention concerns a cladded metal graphic arts impression die plate having a non-magnetic layer of metal integrally joined with a ferromagnetic layer of metal. A relieved, design-defining surface is provided in the outer face of the non-magnetic layer of metal. The graphic arts impression die plate is mounted on a magnetic support member and held in position thereon at least in part by a series of permanent magnets embedded in the magnetic support member in disposition to magnetically attract and hold the ferromagnetic layer of the graphic arts impression die plate supported by the magnetic support member.
The magnetic support member with the cladded metal graphic arts impression die plate thereon is adapted to be affixed to the chase of a stamping or embossing machine such as a sheet or web-fed graphic arts press, in disposition with the design-defining surface of the graphic arts impression die plate in alignment with a predetermined design location.
The utilization of a cladded metal sheet having a non-magnetic layer integral with a ferromagnetic layer for the graphic arts impression die plate facilitates formation of a relieved design in the outer surface of the non-magnetic layer, either by way of a chemical etching process, mechanically using a pantograph milling machine, a computer numerically-controlled (CNC) laser or mechanical milling machine or an operator-controlled milling machine, or by hand-engraving. The cladded metal sheet having a photo-resist coating on the outer surface of the non-magnetic layer of the sheet may be affixed to a magnetic support member through the medium of a series of permanent magnets on the magnetic support member which attract the ferromagnetic layer of the sheet. The magnetic support member and the cladded metal sheet thereon may then be positioned in an etching machine for etching of the exposed areas of the non-magnetic layer of the cladded metal sheet which are not protected by the photo-resist coating. The magnetic support member having embedded permanent magnets therein may also be used to support the cladded metal sheet blank in a chemical etching machine, CNC, pantograph, or operator-controlled milling machines, or during hand engraving, resulting in a design-defining surface. The magnets embedded in the magnetic support member are especially important in stabilizing the central area of the relatively thin cladded metal sheet blank while it is being machined.
2. Description of Related Arts
Stamping dies have long been used in the graphic arts field to apply thin metal foil or thin layers of other transferable material to a substrate such as paper, cardboard, thin metal films or plastic in accordance with a design formed in the stamping surface of the die. Similarly, embossing dies have been provided to emboss or deboss a desired design in a suitable substrate, and to produce lenticular lines, texturing or graining impressions in the paper, plastic, thin metal film or cardboard. Combination dies which combine hot foil stamping or blocking, embossing or debossing, or formation of other surface feature designs are also well known in the art.
Graphic arts impression dies as described have long been prepared by etching or engraving a desired design in the outer surface of a metal plate, usually magnesium, copper or brass. These metal plates generally were of sufficient thickness, as for example about xc2xc in., to cause the plate to be essentially self-sustaining. In the case of relatively long embossing or stamping runs involving as many as hundreds of thousands of impressions, it has been past practice to employ relatively long lived graphic arts impression die plates made of a metal such as copper or brass. For intermediate length runs, the plates were usually made out of magnesium which was less expensive and easier to engrave or etch a relieved design area than with copper or brass.
In those instances where the runs are shorter and any inherent wear of the die surface is acceptable from a final product quality standpoint, non-metal graphic arts impression dies have largely supplanted copper and brass, and even magnesium plates in more recent times by less costly and simpler non-metal dies. For example, steel-backed photo polymer graphic arts impression die plates have been developed in which a hardened photo polymeric composition representing the desired design is supported on a steel backing plate. These steel-backed photo polymer plates can be used with conventional foil stamping and embossing equipment.
Photo polymer graphic arts impression die plates are generally thinner than conventional magnesium, copper or brass graphic arts impression dies, and therefore a spacer plate has been required between the photo polymer graphic arts impression die plate and the chase of the stamping or embossing machine to avoid the necessity of modifying the embossing or stamping equipment. U.S. Pat. No. 5,904,096 (xe2x80x9c""096xe2x80x9d) of May 18, 1999, shows and illustrates one type of spacer plate that can be used to support a photo polymer graphic arts impression die plate on the chase of an embossing or stamping machine. The spacer plate of the ""096 patent is provided with a series of permanent magnets which are described as being capable of magnetically attracting and holding the steel plate portion of the graphic arts impression die plate and thereby the photo polymer die assembly on the spacer plate. Use of a spacer plate of an appropriate thickness serves to support the photo polymer die in the required spaced relationship from the surface of the chase.
There is a need though for a graphic arts impression die which substantially has the longevity of conventional copper or brass dies, yet is less costly and easier to manufacture than conventional metal dies made of copper or brass. There has also been a need for decreasing the make-ready time involved in mounting of a hot foil stamping or blocking, embossing or debossing die on stamping or embossing equipment, particularly from the standpoint of proper alignment of the die with respect to the image onto which the foil is to be applied, or the image to be embossed or debossed. A further important need in the graphic arts impression die field is to provide a die which may be changed out and replaced in the stamping or embossing equipment or apparatus in a significantly shorter period of time than is presently the case.
An improved metal graphic arts impression die is provided which is made up of a cladded metal die plate having a design-defining non-magnetic metal layer such as copper, magnesium, bronze, or other non-ferrous metal which may be cladded to a ferromagnetic support layer that for example may be a steel sheet. A relieved area in the non-ferrous layer defines the design to be foil stamped, embossed, debossed or impressed. In a preferred form, the laminated metal graphic arts die plate has a layer of copper clad to a sheet of carbon steel.
In view of the fact that the laminated die plate is thinner than conventional one-piece magnesium, copper or bronze stamping dies or embossing dies, a die plate support is preferably provided for holding the laminated die plate on the chase of a foil stamping or embossing machine. An improved magnetic support plate is provided for the steel-backed, graphic arts impression die assembly made up of a non-ferrous support member having a die mounting surface which substantially complementally receives the cladded steel or steel-backed graphic arts impression die. A plurality of specifically spaced magnetic elements are embedded in the support member substantially through the full extent thereof. The attractive force of the steel backing to the magnetic surface of the support plate is enhanced by positioning of the magnets embedded in the support member such that adjacent pairs of the magnets have their north and south poles oriented oppositely, and a ferro-magnetic component is positioned in bridging relationship to each pair of magnets against the faces thereof opposite the die support face of the plate to enhance the magnetic flux emanating from each of the pairs of magnets.
The provision of a magnetic plate for supporting a steel-backed impression die has a major benefit in the use of the assembly in that minute adjustments in the position of the die on the support plate after mounting of the assembly on the chase of the sheet or web-fed press may be accomplished with greater facility and more rapidly than in past mounting practices wherein repositioning of the die could be accomplished only by time-consuming manipulation of a number of fastening devices.
In a preferred embodiment of the invention, the magnets are of square shape, with each pair of magnets being in specifically spaced relationship from one another, and from adjacent pairs of magnets. The magnets of each pair are positioned such that their north and south pole axes extend through the major faces of each of the magnets, with the length and width dimensions of each of the magnets being substantially greater than the thickness of each magnet. The ferro-magnetic component is preferably in the nature of a steel plate that extends between and engages the major face of each of the magnets which is most remote from the die mounting surface of the support member.
The steel strip which extends between and engages the major face of each of the magnets most remote from the die mounting surface of the support member, enhances the holding power of the bridged magnets by directing and concentrating the magnetic field surrounding those ends of the magnets in closest proximity to the die assembly supporting surface of the support member. The ferro-magnetic component also functions to decrease the flux leakage from the magnets at the perimeter of the magnetic field created by respective pairs of magnets.
The individual magnets are embedded in the non-ferrous support member in positions causing the major faces thereof in closest proximity to the die mounting surface of the support member to be spaced inwardly from the plane of the outer die mounting surface. The magnets are not however spaced so far from the die mounting surface to significantly decrease the magnetic attractive flux of the magnets or the die assembly. In this way, the magnets are protected against wear or breakage during the frequent attachment to and detachment of the magnetic support plate graphic arts die assemblies from the magnetic support member. Furthermore, a smooth and consistent outer die support surface is presented that is not interrupted by the outer surface of the magnets to thus minimize any distortion of the design-defining layer.
The magnetic support member of this invention is also useful to support a cladded steel or steel-backed graphic arts impression die made up of a non-ferrous, design-defining layer backed by steel during removal of material from the surface of the non-ferrous layer by etching to form the design image in the outer surface thereof. Where the design-defining image is produced by a chemical etching process, a photo-resist composition is first applied to the outer surface of the non-ferrous layer of the cladded metal sheet. The photo-resist composition is configured to define the portion of the non-ferrous layer which is not to be removed by an etchant solution in the etchant bath equipment.
A magnetic die support plate for the graphic arts support die is preferably fabricated of plastic or other etchant-resistant material and is provided with a series of pairs of permanent magnets embedded therein as described and in disposition to magnetically attract the steel layer of the cladded metal sheet to at least partially hold the cladded metal die on the die plate support. The assembly of the cladded metal die plate with the photo-resist composition on the outer face of the non-ferrous layer of the die plate, and the support for the die plate may then be placed in an etchant machine to effect etching of a desired design in the outer surface of the non-ferrous layer.
Upon completion of the etching step and removal of the photo-resist composition from the surface of the non-ferrous layer of the cladded metal die plate, the die plate is ready for attachment to the spacer plate and then to the chase of the embossing or stamping machine.